A full-scale evacuation of the Georgian city of Gori has started as fears rose that Russia would soon advance its troops across the border from the breakaway republic of South Ossetia into the main body of Georgia itself.

Any such incursion would be a dangerous escalation of a conflict that has already reportedly claimed thousands of lives and displaced thousands more. Russia regained total control of Tskhinvali, the capital of South Ossetia, and Georgia offered a unilateral ceasefire as it withdrew all its troops.

International opinion hardened against Russia, which has been roundly accused of a “disproportionate reaction” to Georgia’s move into South Ossetia last week. Jim Jeffrey, the US’s deputy National Security Advisor, told reporters: “We have made it clear to the Russians that if the disproportionate and dangerous escalation on the Russian side continues, that this will have a significant long-term impact on US-Russian relations.”

But American diplomats conceded that the US had few options and ruled out military intervention on behalf of Georgia. “We have no good options,” a US National Security Council official told The Daily Telegraph. “We need Russia’s co-operation over Iran and derailing that over a localised conflict in Georgia makes no sense. We just have to hope that diplomacy prevails. The next necessary step is for Russia to respond positively to Georgia’s ceasefire declaration.”

Russian Foreign Minister Sergei Lavrov told US Secretary of State Condoleezza Rice that Mikheil Saakashvili, the president of Georgia, “must go”. Mr Lavrov said Russia would continue its military action in South Ossetia due to the “continuing direct threat to Russian citizens”.